The invention relates to a method for preventing sidewall indentations in the splice area between two ends of a tire carcass and to a device for making and testing tire carcass splice samples and for measuring side wall indentations occuring therein during the inflating of the tire.
With conventional vehicle tires the splice regions defined at the connection of the ends transversal to the cords of the tire carcass fabric are secured by more or less cord overlapping of the edges of the carcass. However due to this technique the tire carcass can be disturbed and thermal shrinkage behaviour in the region of overlapping cords may occur during the inflation of the tire. The carcass fabric with high thermal shrinkage could therefore, when removed from the curing or vulcanizing mold, have considerable shrinkage in the splice region, which would result in side wall indentations in the tire.
The use of the carcass fabric of polyester, Nylon or Rayon with low shrinkage values would provide dimension-stable tires. However with operating pressure of 2 bars or under the influence of the sunlight or during the treatment of the car in a paint-baking oven, the carcass expansion value would be up to 50% lower at the splice, as compared to the normal tire carcasses. This difference will definitely show up in an increased sidewall indentation.
One of conventional methods of the type under discussion has been disclosed in U.S. Pat. No. 4,466,473. With this known method, the carcass cords of one side of the overlapping carcass splice are cut at uniform intervals from each other and the disturbing effect of shrinkage and elongation is substantially reduced. The disadvantage of this known method resides in that the cutting of the cords of the carcass fabric and the making of the splices at the splice table as well as later on the tire building stand can only be achieved with a great effort.
It is also not very simple to ensure the depth of the cut during the cutting of the cords when the carcass cut edge does not run straight to the cords of the carcass. There is also the danger that the incised cords would not precisely lie under the cords of the other carcass half during the splicing process, and weak spots would result.